7 Dead, At Least 17 Wounded In Hours-Long Fights At S.C. Prison : The Two-WayOfficials have not said what might have sparked the violence, which is the latest in a string of incidents at the South Carolina prison. No prison staff members were injured.

A sequence of fights that raged for more than seven hours at a South Carolina prison left seven inmates dead and at least 17 more needing "outside medical attention," the South Carolina Department of Corrections said early Monday.

The incident at Lee Correctional Institution in Bishopville, S.C., "involved multiple inmate on inmate altercations in three housing units," the Department of Corrections said. No prison staff were injured.

The fights began at 7:15 p.m. ET Sunday; the facility wasn't secured until 2:55 a.m. on Monday, prison officials say. Multiple local and state agencies rushed to help at the facility, which is located in a rural area just north of Interstate 20, about an hour east of Columbia.

Lee County Fire and Rescue says it assisted in a mass casualty situation at Lee Correctional, adding that other emergency crews from neighboring counties — including some that are roughly 40 miles away — also pitched in.

Lee County Fire/Rescue assisted With a Mass Causality Incident at Lee Correctional. Mutual Aid was received from FlorenceCounty EMS, Kershaw County EMS, Darlington County EMS, Lexington County EMS and Hartsville Rescue. Assistance was also received from Med One a private service. pic.twitter.com/P22A1ruzQY

Lee Correctional Institution is a Level 3 facility — meaning it's high security and holds violent offenders who are serving long sentences, as well as those with behavioral problems, the Department of Corrections says. The prison opened in 1993.

Officials have not said what might have sparked the violence, which is the latest in a string of incidents at the prison.

"Sunday's deadly incident came three weeks after inmates briefly held an officer hostage and took control of part of a dorm at the Bishopville prison," The State newspaper reports.

The State adds that one inmate died in fights there in both 2017 and 2016 and that five inmates were injured in a separate fight in 2016.